The high-tech hunt for James Foley's killer

WHO killed James Foley? Last week, militants from Islamic State, previously known as ISIS, released a clip of a masked man appearing to behead the American journalist.

Scotland Yard and the FBI have teamed up to hunt down the man in the video. In an interview on CNN on Sunday, Peter Westmacott, the British ambassador to the US, said that the killer was close to being identified, thanks in part to voice-recognition technology. Software can be used to compare the resonance of someone's speech with other voices in a government database to provide a list of suspects.

But human experts will be needed to narrow down the list on the basis of features such as voice quality, rhythm, grammar choice and the way the assailant pronounces different consonants and vowels, says freelance forensic voice-analyst Elizabeth McClelland. "It's not like a fingerprint," says McClelland. "It's more an art than a science." She thinks the man has an accent characteristic of London or south England, with quirks that indicate he has been educated in the UK and might speak a foreign language, such as Farsi.

The heavily edited video is being scoured for visual clues too. "It's like a jigsaw puzzle," says Stuart Ray, an imagery analyst at McKenzie Intelligence Services in London. "You need lots of different pieces to fall into place."

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